The long range objective of the proposed research is to determine the three-dimensional structure and function of a leucine, isoleucine, valine-binding protein. This protein is a member of a family of proteins which are essential components of the high affinity active transport systems in E. coli. Further interest on this group of proteins stems from the fact that some of the same proteins are also components of chemotaxis. In order to solve the structure, we have been screening potential heavy atom derivatives. Two derivatives--K2PtCl4 and SmCl3--have been obtained. This grant also supports a similar study on the sulfate-binding protein. In this case, two heavy atom derivatives have been solved.